Patented Jan. 16, 1951 2,538,417 UNITED STATES PATENT of FICE 2,538,417 INDIUM PLATING David Frederick Green and London, England, assignorsJohn Ernest.to Vandervell Salmon, Products Limited, London, England No Drawing. Application November 7, 1945, se rial. No. 627,278. In Great-Britain January 2, 1945 6 Claims. (CL 204-45). 1. 2 This invention relates to indium plating par orated until crystallisation of indium chloride ticularly in its relation to electroplating bearing occurs, and the crystallised indium chloride is Surfaces. Y - w then dissolved in distilled water, a second solu In the specification of our U. S. application Ser. tion of potassium-cyanide" and sorbitol in water. No. 604,524, now Patent No. 2,497,988, dated Feb and a third solution of potassium-hydroxide in ruary 21, 1950, a stable electrolytic bath is de water are then prepared, the first solution is then Scribed which consists of an indium salt, alkali added to the second solution drop by drop ac metal cyanide and hydroxide and dextrose or companied by constant stirring and the third other suitable saccharide. While other indium Solution is then added. The quantities of the Salts may be used the use of the chloride is pre materials used being selected to obtain a stable ferred. Our research has established that it is Solution. An example of these quantities which not necessary to use a saccharide as laid down in has proved satisfactory is as follows: our prior specification above referred to, but that Indium metal, 30 grammes other materials such as certain polyhydric al Potassium-cyanide, 100 grammes or approxi cohols can be used and Sorbitol has been found s mately 2 moles particularly suitable. The sorbitol can be sub Sorbitol, 30 grammes stituted for dextrose in the solutions described in Potassium hydroxide, 120 grammes or approxi our prior specifications in similar concentrations mately 2 moles and Solutions So prepared can be used to prepare a solid residue which can be stored and trans 20 to make 1 litre of solution. ported conveniently and then used to reconstitute We claim: a plating solution merely by dissolving in Water 1. A Solid Soluble mixture adapted to be dis and adjusting the free alkali metal cyanide and Solved in water to produce an electrolytic indium hydroxide contents to the desired concentrations. plating bath which comprises indium, Sorbitol, Alternatively, if desired, sufficient alkali metal 25 alkali metal hydroxide and alkali metal cyanide cyanide and hydroxide can be mixed with the in or about the following proportions: 30 solid so that when dissolved in water it will yield grammes of indium as indium trichloride, 2 moles a solution containing the desired concentrations Of alkali metal cyanide, 30 grammes of Sorbitol of free alkali metal cyanide and hydroxide. The and approximately 2 moles of an alkali metal hy amount of cyanide and hydroxide required can 30 droxide. easily be determined by dissolving a Small portion 2. A Solid Soluble mixture adapted to be dis of each batch in the appropriate quantity of water Solved in water to produce an electrolytic indium and analysing the solution. - - plating bath which comprises indium, sorbitol, Our invention may be said to consist of: potassium hydroxide and potassium cyanide in or An electrolytic bath for use in electroplating about the following proportions; 30 grammes of with indium according to which sufficient alkali indium as indium trichloride, 30 grammes of sor metal hydroxide is added to an electrolytic bath bitol, 100 grammes of potassium cyanide and 120 consisting of an indium salt, alkali metal cyanide grammes of potassium hydroxide. and sorbitol or equivalent polyhydric alcohol to 3. A Solid Soluble mixture adapted to be dis provide a stable solution. 40 Solved in Water to produce an electrolytic indium The invention further comprises a process of plating bath which comprises indium, sorbitol, electroplating with indium wherein such an elec Sodium hydroxide and Sodium cyanide in or about trolytic bath is used. the following proportions: 30 grammes of indi Suitable hydroxides for use in the process are um as indium trichloride, 30 grammes of sorbitol, Sodium or potassium hydroxide, and the indium 2 moles of sodium hydroxide and 2 moles of sodi salt employed is preferably indium chloride. um cyanide. One specific electrolytic bath for use in plating 4. A method of making a water soluble mixture metals with indium, according to Our invention, for use in preparing an indium electroplating consists of a stable composition of indium, potas bath according to which 30 grammes of indium sium cyanide, potassium hydroxide and SOrbitol. 50 as indium trichloride is added to a solution con According to one method of prepairing Such an taining approximately 2 moles of alkali metal electrolytic bath comprising indium-potassium cyanide and 30 grammes of Sorbitol and approxi cyanide-potassium hydroxide and sorbitol the in mately 2 moles of an alkali metal hydroxide in dium metal is first dissolved in an excess of con which the indium solution is added to a mixture centrated hydrochloric acid and thesolution evap s 5 of the sorbitol and cyanide accompanied by agita 2,538,417 3 4. tion and subsequently the hydroxide is added and is evaporated to dryness to leave a residue soluble the Solution is evaporated to dryness to leave a in water. residue soluble in water. DAVID FREDERICK GREEN. 5. A method of making a water soluble mix JOHN ERNEST SALMON. ture for use in preparing an indium electroplat ing bath according to which 30 grammes of in REFERENCES CTED dium as indium trichloride is added to a solution The following references are of record in the containing approximately 100 grammes of potas file of this patent: sium cyanide and 30 grammes of Sorbitol and ap proximately 120 grammes of potassium hydroxide 0. UNITED STATES PATENTS in which the indium Solution is added to a mix Number . . Name Date ture of the Sorbitol and cyanide accompanied by 694,658 Meurant ------Mar. 4, 1902 agitation and Subsequently the hydroxide is added 1849,293 Gray ------Mar. 15, 1932 and the solution is evaporated to dryness to leave 1965,251 Murray et al. ------July 3, 1934 a residue soluble in water. s 2,423,624 Smart ------July 8, 1947 6. A method of making a water soluble mixture 2,458,839 Dyer et al. ------Jan. 1, 1949 for use in preparing an indium electroplating bath according to which 30 grammes of indium ... FOREIGN PATENTS as indium trichloride is added to a solution con Number Country Date taining approximately 2 moles of Sodium cyanide 573,848 Great Britain ------of 1945 and 30 grammes of Sorbitol and approximately 2 moles of sodium hydroxide in which the indium OTHER REFERENCES solution is added to a mixture of the Sorbitol and iron Age, Dec. 19, 1940, pp. 35-38. cyanide accompanied by agitation and subse Transactions of Electrochemical Society, vol. quently the hydroxide is added and the solution 25 65, pp. 377-383 (1934).